Method for treating circuit board for use in disk recorder or player apparatus

ABSTRACT

A circuit board is mounted in a cabinet in which a disk is housed. A treatment for preliminarily releasing ammonia possibly causing fogging of the disk from the circuit board is performed by allowing the circuit board to stand at 70° C. outside the cabinet for 24 hours before the circuit board is mounted in the cabinet.

TECHNICAL FIELD

The present invention relates to a method for treating a circuit boardfor use in a disk recorder or player apparatus.

BACKGROUND ART

FIG. 2 is a sectional view of a conventional disk recorder or playerapparatus. A disk 60, which is a magneto-optical disk, is rotatablyhoused in a cartridge 6 having openings formed in upper and lower facesthereof. A turn table 70 and a pickup 7 movable toward and away from theturn table 70 are provided on a chassis 1 which receives the cartridge6. A recording head 72 is attached to the pickup 7 via a head lever 71.A portion of the disk 60 is irradiated with a beam from the pickup 7thereby to be heated at a Curie temperature and, at the same time, anupper surface portion of the disk 60 is magnetized by the recording head72 for recording a signal therein. In signal reproduction, the disk isirradiated with a beam from the pickup 7, and the level (0-level or1-level) of a recorded signal is determined on the basis of thediffractive direction of a light beam reflected on the disk.

The chassis 1 and the cartridge 6 are housed in a cabinet 2 constitutedby cabinet halves 20, 21 which are vertically combined together. Acircuit board 3 for energization of the pickup 7 and the turn table 70is provided in the lower cabinet half 21. The circuit board 3 iscomposed of a glass epoxy resin or the like. It is noted that theposition of the circuit board 3 is not limited to that shown in FIG. 2.

Since circuit components (not shown) mounted on the circuit board 3generate heat during the signal recording and reproduction, the internaltemperature of the cabinet 2 is liable to rise. In view of the rise ofthe internal temperature of the apparatus, the applicant of the presentinvention intends to guarantee that the apparatus normally operates at atemperature up to 70° C., and checks the apparatus to confirm that theapparatus does not malfunction at a temperature of 70° C. or lower whenthe apparatus is mass-produced.

The applicant found that the apparatus suffered from the followingproblem.

The applicant found that, when the apparatus was left at a hightemperature, the surface of the disk 60 was fogged so that the C/N ratioof the reproduced signal was reduced or the disk 60 was not accuratelymagnetized in the recording. The applicant analyzed a substancedeposited on the surface of the disk 60, and found that the majorcomponent of the substance was ammonium sulfate (NH₄)₂SO₄. However, noneof the components provided in the apparatus were produced by employingammonium sulfate, and there was no evidence that ammonium sulfateexternally adhered onto the disk.

The applicant investigated the mechanism of the generation of ammoniumsulfate and, as a result, found that ammonium sulfate was generated bythe following chemical reactions.

As described above, the circuit board 3 is composed of the glass epoxyresin. Further, cases of the mounted circuit components are oftencomposed of an epoxy resin. As well known, the epoxy resin issynthesized from bisphenol-A having a molecular formula (CH₃)₂C(C₆H₄OH)₂and epichlorohydrin C₃H₅OCl.

Therefore, if the epoxy resin is left at a high temperature for a longperiod of time, bisphenol-A is decomposed and modified to undergocondensation polymerization, so that some of functional groups areremoved from bisphenol-A. As a result, water and ammonia are generatedas by-products. Ammonia NH₃ is present in the form of molecules in atrace amount, but reacts with sulfur dioxide gas present in theatmosphere to provide ammonium sulfate (NH₄)₂SO₄ as follows:SO₂+H₂O+O→H₂SO₄H₂SO₄+2NH₃→(NH₄)₂SO₄

That is, the applicant found that, where the circuit board 3 was left ataround the operation guarantee temperature (70° C.) for a long period oftime, ammonia is generated and, as a result, the disk 60 was fogged.With a recent trend toward the size reduction and thickness reduction ofthe apparatus, the cabinet 2 has a higher internal temperature.Therefore, an ammonia concentration in the cabinet 2 tends to beincreased, making the disk more liable to be fogged.

It is an object of the present invention to prevent the fogging of thedisk even if the disk is left at a high temperature in the apparatus fora long period of time.

DISCLOSURE OF THE INVENTION

A treatment for preliminarily releasing a substance possibly causingfogging of a disk 60 from a circuit board 3 is performed by allowing thecircuit board 3 to stand in a predetermined high temperature environmentoutside a cabinet 2 for a predetermined period of time before thecircuit board 3 is mounted in the cabinet 2.

The circuit board 3 is allowed to stand in the predetermined hightemperature environment for the predetermined period of time before thecircuit board 3 is mounted in the cabinet 2. Thus, the substancepossibly causing the fogging of the disk 60 is released outside thecabinet 2. This prevents the fogging of the disk, thereby diminishingthe possibility of causing a trouble in signal recording andreproduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a chamber and a container;

FIG. 2 is a sectional view of a conventional disk recorder/playerapparatus; and

FIG. 3 is a front view of a detection tube.

BEST MODE FOR CARRYING OUT THE INVENTION

One embodiment of the present invention will hereinafter be describedwith reference to the attached drawings.

A disk recorder or player apparatus has the same construction as theapparatus shown in FIG. 2. This embodiment is characterized in that thecircuit board 3 is heat-treated before it is mounted in the cabinet 2.

The applicant heat-treated the circuit board 3 for a predeterminedperiod of time to determine the amount of ammonia released from thecircuit board 3 when the apparatus was kept at a high temperature.First, all circuit boards 3 to be mounted in the apparatus were put in acontainer 4 as shown in FIG. 1, and the container 4 was sealed. Thecontainer 4 was allowed to stand at 80° C. for one hour. Then, thecontainer 4 was opened, and the ammonia concentration of air in thecontainer was measured by means of a detection tube. At this time, theammonia concentration was 2 PPM. That is, 2 PPM of ammonia was releasedin one hour.

Here, the detection tube is a tube 5 filled with a detection agent andhaving a scale 50 provided on the surface of the tube 5 as shown in FIG.3. When the air to be subjected to the measurement is introduced intothe tube 5, the detection agent reacts with ammonia and is partlychanged in color. Then, the length of a portion of the detection agentchanged in color is measured by the scale 50. Thus, the concentrationcan easily be determined.

Since ammonia is rarely present in the atmosphere, a concentration of 2PPM is very high. Therefore, the ammonia concentration in the cabinet 2is increased if the apparatus is kept at the high temperature.

Experiment 1

In view of this data, the applicant came up with an idea that it wouldbe possible to preliminarily remove ammonia by allowing the circuitboard 3 to stand at a high temperature for a predetermined period oftime before mounting the circuit board 3 in the cabinet 2. The applicantconsidered that it would be desirable to set the temperature conditionas high as possible. The upper limit of the operation guaranteetemperature of the circuit components mounted on the circuit board 3 is70° C. If the circuit board 3 is left at a temperature higher than 70°C. for a long period of time, there is a possibility that the mountedcircuit components malfunction. Therefore, the temperature at which thecircuit board is allowed to stand for a long period of time was set at70° C.

The applicant allowed three circuit boards 3 to stand in a large volumechamber 8 kept at an internal temperature of 70° C. for 12 hours, for 24hours and for 48 hours, respectively. Thereafter, the circuit boards 3were each allowed to stand in the container 4 kept at an internaltemperature of 80° C. for one hour, and an ammonia concentration in thecontainer 4 was measured. Of course, the chamber 8 and the container 4were located outside the cabinet 2. Data obtained by the measurement ofthe ammonia concentration is shown in Table 1.

TABLE 1 Period (at 70° C.) Ammonia concentration in chamber 4 12 hours0.3 to 0.4 PPM 24 hours 0.2 PPM 48 hours 0.15 to 0.2 PPM

As indicated by the above data, the concentration of ammonia released inthe container 4 after the circuit boards were left in the chamber 8 at70° C. for 24 hours or for 48 hours was about 0.2 PPM. Therefore, theammonia concentration was reduced to about 1/10 as compared with a casewhere the circuit boards were not allowed to stand in the chamber 8. Theerrorless measurement limit of the detection tube is about 0.1 PPM, sothat the ammonia concentrations after the circuit boards were left for24 hours and for 48 hours are regarded to be virtually equivalent toeach other. Therefore, the applicant expected that sufficientlyeffective measures against the fogging of the disk 60 would be providedby mounting the circuit board 3 in the cabinet 2 after allowing thecircuit board 3 to stand at 70° C. for 24 hours. The concentration ofammonia released in the chamber 8 was not measured, but supposedly about1.8 PPM (=2−0.2).

Experiment 2

The applicant allowed three circuit boards 3 to stand in the chamber 8for 12 hours, for 24 hours and for 48 hours, respectively, insubstantially the same manner as described above, except that theinternal temperature of the chamber 8 was changed to 60° C. Thereafter,the circuit boards 3 were allowed to stand in the container 4 kept at aninternal temperature of

FIG. 2 is a sectional view of a conventional disk recorder/playerapparatus; and 80° C. for one hour, and an ammonia concentration in thecontainer 4 was measured. Data obtained by the measurement is shown inTable 2.

TABLE 2 Period (at 60° C.) Ammonia concentration in chamber 4 12 hours0.5 PPM 24 hours 0.2 to 0.3 PPM 48 hours 0.2 to 0.3 PPM

As indicated by the above data, the concentrations of ammonia releasedin the container 4 after the circuit boards were left in the chamber 8for 24 hours and for 48 hours were virtually equivalent to each otherand about 0.2 PPM. It is considered that the adverse effect of heat onthe mounted circuit components is suppressed in the case where thecircuit boards are left at 60° C., as compared with the case where thecircuit boards are left at 70° C. The applicant used a circuit board 3treated by allowing the circuit board 3 to stand in the chamber 8 at 60°C. for 24 hours and then in the container 4 kept at 80° C. for one hour.

The circuit board 3 was mounted in the cabinet 2 after being subjectedto the heat treatment according to the embodiment, whereby ammoniareleased from the circuit board 3 in the cabinet 2 was drasticallyreduced. The applicant observed the disk 60, and found that no ammoniumsulfate adhered on the disk 60 or the amount of ammonium sulfateadhering on the disk 60 was drastically reduced. Thus, the signalrecording or reproduction on the disk 60 can be stabilized.

1. A method for treating a circuit board to be mounted in a cabinet of adisk recorder or player apparatus in which a disk is housed, forreleasing from the circuit board a substance possibly causing fogging ofthe disk by a chemical reaction at a high temperature, the methodcomprising the step of allowing the circuit board to stand in apredetermined high temperature environment outside the cabinet for apredetermined period of time before the circuit board is mounted in thecabinet to preliminarily release the substance possibly causing thefogging of the disk from the circuit board.
 2. A method as set forth inclaim 1, wherein the substance possibly causing the fogging of the diskis ammonia.
 3. A method as set forth in claim 1, wherein thepredetermined high temperature environment in which the circuit board isallowed to stand before the circuit board is mounted in the cabinet iskept at a temperature which is not higher than an operation guaranteetemperature of the disk recorder or player apparatus.